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Observing Double Stars

A season by season list of finely colour contrasted double stars to illustrate star colours at all times of the year.

Double stars can be among the best objects to observe in the night sky. They represent some of natures best kept secrets in astronomy. Beautiful variations in colour and brightness are a joy to observe. Please take an opportunity to observe some if you are able.

The Table below lists some glowing examples ( please excuse the pun.) of objects to give you a flavour of this vast and seldomly viewed subject

Double Stars

Name

Colours

Magnitudes

Separation

Right Ascension

Declination

55 Piscium

OR + BL

5.5 + 8.2

6.6

0hrs 39.9mins

+21deg 26.4mins

gamma Andromeda

GOLD + BL

3.0 + 5.0

9.7

2hrs 3.9mins

+42deg 20mins

6 Trianguli

YELL + BL

5.0 + 6.4

3.9

2hrs 12 mins

+30deg 18mins 27

32 Eridani

TOPAZ + GREEN

4.0 + 6.0

7.0

3hrs 52mins

-2deg 57mins

20 Geminorum

YELL + BL

6.3 + 6.9

20.0"

6hrs 23.3mins

+17deg 47mins

iota Cancri

YELL + BL

4.1 + 6.0

30.7"

8hrs 46.7mins

+28deg 46mins

88 Leonis

YELL + LILAC

6.3 + 9.1

15.4"

11hrs 31.7mins

+14deg 22mins

Epsilon Bootis *

YELL + BL

2.6 + 4.8

2.9"

14hrs 45.0mins

+27deg 04mins

alpha Herculis

OR + GREEN

3.5 + 5.4

4.8"

17hrs 14.6mins

+14deg 23mins

39 Orphiuchi

OR + BL

5.2 + 6.6

10.0"

17hrs 18mins

-24deg 17mins

beta Cygni **

YELL + BL

3.0 + 5.3

34.7"

19hrs 30.7mins

+27deg 58mins

gamma Delphini

YELL + EMERALD

4.4 + 5.0

9.1"

20hrs 46.7mins

+16deg 07mins

delta Cephi ***

YELL + BL

4.2 + 6.1

40.6"

22hrs 29.2mins

+58deg 25mins

Notes:

* Epsilon Bootis needs a fine night and first class conditions owing to the big brightness difference and the small separation but is beautiful.

** beta Cygni grand contrast, most beautiful when seen against the rich starry background, shown by a low power wide field eyepiece on a moonless night Albireo

*** Delta Cephi is the prototype Cepheid variable ; about 5 degrees to the west lies the garnet star mu cephei, perhaps the reddest star visible to the unaided eye from the UK , an irregularly variable red super giant

In addition the many double stars showing subtler colour differences can often be just as beautiful but the above have been chosen to make the point re; different star colours for the delight of the observer.

A point which can be further emphasised by switching between one of the above and one of the fine double stars showing little or no colour contrast e.g. gamma arietis, theta serpentis, gamma virginis, alpha geminorum, gamma leonis